The present invention relates to infusion apparatus, and particularly to a drip chamber used in such apparatus.
Infusion apparatus commonly includes drip chambers into which the liquid is introduced in the form of drops to enable visually monitoring the rate of flow of the infusion liquid. However, one of the dangers of using drip chambers is the possibility that the air within the drip chamber may enter the infusion liquid passing into the patient's body. This danger is particularly significant when the infusion sets are employed in the field, for example on a battlefield or during a disaster involving rough handling conditions, or when high rates of infusion are to be administered.
My U.S. Pat. No. 3,744,492 describes a drip chamber constructed particularly to prevent the entry of air bubbles into the infusion liquid under such conditions. That apparatus comprises a portable housing defining a drip chamber therein, an inlet connector leading from the upper end of the chamber for connection to a source of infusion liquid, an outlet connector leading from the lower end of the chamber for connection to an infusion device, and an outlet tube supported within the chamber with the lower end of the outlet tube leading to the outlet connector and the upper end of the outlet tube located at an intermediate portion of the chamber spaced below the inlet connector. The provision of the outlet tube projecting into the drip chamber produces a seal which, during the administration of the infusion, prevents the escape of air bubbles from the drip chamber into the infusion device even though the infusion set is shaken or inclined such that the vertical axis of its drip chamber deviates from the true vertical.
Drip chambers according to the construction of the above-described patent are satisfactory for most conditions of use, but not for field or rescue conditions. Thus, it was found that when the infusion was administered at a high rate and under exceptionally rough handling conditions, for example when subjected to rapid vibrations as might occur during the administration of the infusion liquid while the subject was being carried by a land or air vehicle (e.g., a helicopter), the rapid vibrations increased the turbulence of the infusion liquid such that there was produced, at the upper end of the outlet tube, a low pressure area or "funnel" which tended to draw into it air from the drip chamber, resulting in the entrainment of air bubbles in the infusion liquid.
Examples of other known types of liquid infusion devices are described in Ford U.S. Pat. No. 2,675,000 and Butler U.S. Pat. No. 2,729,212. The devices described in those patents, however, are not suitable for use at high flow rates and/or during the above-mentioned rough handling conditions, since if they were so used they would tend to entrain air into the administered liquid.